Chromatography

Purpose :
To separate and identify the colours found in a type of commercial food dye.

Theory :

Chromatography is a technique used to separate the different components in a mixture. All chromatography techniques consists of two major components : the stationary phase and the mobile phase. The method consists of dissolving the mixture in a suitable solvent and which is then carried over the surface of the stationary phase.

Separation is possible because different substances have different degrees of absorption or solubility between the stationary and the mobile phase. The component will move along the stationary phase at different speeds, and thus separated. In paper chromatography, the stationary space is the strip of chromatography paper and the mobile phase is suitable solvent.

By comparing the Rf value of the component with the Rf value of known substances, the component in the mixture can be identified. The value of Rf for each of the component in the mixture can be identified. The value of Rf for each of the component is calculated using the formula :

1. 100 cm3 of ethanol and water solvent was prepared in the ratio of 3:1. 2. The solvent was poured in a 1 dm3 tall container. 3. The mouth of the container was covered with plastic and it was leaved to stand for 30 minutes. 4. A line was lightly marked with a pencil about 2 cm from one end on a strip of filter paper measuring about 4 cm wide and 38 cm long. 5. The solution of food dye was spotted onto a marked spot in the middle of the line as shown in the diagram by using a fine glass capillary pipette. (Refer to Figure 1)